It is well known to smear a liquid on a slide and then subject the liquid to examination under a microscope. This is done widely, for example, with blood to make a white blood cell differential count. The quality of the smear is important, for example, automatic blood cell differential analyzers cannot provide an accurate white blood cell differential count unless there is an adequate uniform area of blood cell monolayer in the smear. Not only is it important to provide a good smear, but it is also important to provide a uniformity of smear from one slide to another.
Prior art devices for smearing a slide are shown in the following patents: German Patent No. 439,124, Jan. 24, 1927; U.S. Pat. No. 3,683,850, Aug. 15, 1972; and U.S. Pat. No. 3,880,111, Apr. 29, 1975. The device of the German patent is markedly different structurally and is unsatisfactory since it is not possible manually to control the speed of the spreader while smearing to provide either a good smear or smears which are uniform from one smear to the other. While U.S. Pats. Nos. 3,683,850 and 3,880,111 disclose satisfactory devices they are markedly different structurally and lack the highly advantageous features provided by the invention. While slide magazines are known the prior art fails to teach the employment of a slide magazine which permits smearing a liquid on a slide in the magazine. The magazine eliminates unwanted touching of the slides and provides for the easy removal of a slide after it is smeared. Spreader wear is markedly reduced by keeping the spreader out of contact with the slide until it approaches the point on the slide where it is to contact the liquid. The device of the invention has novel means to slow the advance of the spreader as it approaches the position on the slide where the liquid is to be contacted. While manually actuated, the invention provides automatic timing of the dwell time for the spreading of the liquid on the spreaders. Novel means are provided for varying the angles of the spreaders to provide a wedge smear.